Parkinson's disease (PD) is characterized by a selective degeneration of dopaminergic neurons in the substantia nigra, resulting in irreversible motor dysfunction. While the pathology of the disease is well established, the cellular mechanisms underlying the degeneration of dopaminergic neurons remain enigmatic. Evidence from cell culture studies, animal models, and post-mortem analyses consistently demonstrates that apoptosis is the major mode of cell death in PD, in which oxidative stress might play a critical role. The key markers of dopaminergic cell death, including reactive oxygen species (ROS) generation, caspase-3 activation, and DNA fragmentation, have been extensively evaluated. However, little is understood about the downstream cellular events of caspase-3 activation that lead to DNA fragmentation. As outlined in the preliminary data, we have identified that protein kinase C-delta (PKCd), a member of the novel PKC isoform family, is an oxidative stress kinase that is highly expressed in nigral dopaminergic neurons and serves as a key substrate for caspase-3. PKCd is proteolytically cleaved into regulatory and catalytic subunits by caspase-3 to persistently increase its kinase activity, which further contributes to apoptosis in cell culture models of PD. Therefore, we will extend our preliminary findings by pursuing the following specific aims: (i) To systematically characterize the caspase-3 dependent proteolytic activation of PKCd and its role in dopaminergic neuronal apoptosis in animal models of Parkinson's disease, (ii) To investigate whether tyrosine phosphorylation of PKCd by non-receptor tyrosine kinases during oxidative stress promotes the caspase-3 dependent proteolytic activation of PKCd to induce apoptosis in dopaminergic neurons. If so, identify the upstream tyrosine kinase that regulates the proapoptotic function of PKCd, (iii) To establish the proapoptotic function of PKCd in nigral dopaminergic degeneration using PKCd knockout (PKCd -/-) C57 black mice, and (iv) To determine the potential neuroprotective effects of the PKCd inhibitor rottlerin, non-receptor tyrosine kinase inhibitors, and siRNA against PKCd in the MPTP mouse model of PD. Cellular, molecular, and behavioral approaches will be used to delineate these specific aims. Together, results from the proposed systematic investigation will illuminate the cellular mechanisms underlying the oxidative stress dependent apoptotic cell death process in dopaminergic degeneration, and this knowledge will advance the development of more targeted and innovative therapeutic strategies for the treatment of PD.